Apparent sulfur-free color protection method for mature tremella aurantialba sporocarp

Abstract

The invention discloses an apparent sulfur-free color protection method for mature tremella aurantialba sporocarp, and relates to the technical field of edible mushroom color protection methods. The method comprises the following steps: preparing a composite color fixative from 30 mg / mL food-grade L-malic acid and citric acid according to a mass ratio of 2: 1 or 1: 2, uniformly cutting tremella aurantialba fruiting bodies into blocks, and soaking the blocks in the composite color fixative for 20 minutes. According to the method, the food-grade additive with low price and high safety is used, and the method has the advantages of simplicity and convenience in operation, low cost, no sulfur dioxide and the like. The optimal ratio of the composite color fixative provided by the invention has a remarkable color protection effect on the color of the fruiting bodies of the tremella aurantialba in the mature period, solves the problem of color change in the storage and processing processes of the fruiting bodies of the tremella aurantialba, prolongs the shelf life, and further improves the value of the tremella aurantialba in subsequent development and application.

Description

Technical Field

[0001] The invention relates to the technical field of edible fungi color protection methods, and in particular to an apparent sulfur-free color protection method for mature golden fungus fruiting bodies, which is used for extending the shelf life of golden fungus fruiting bodies and improving the apparent properties of golden fungus fruiting bodies during production, processing, storage and transportation. Background Art

[0002] Golden ear (Naematelia aurantialba) belongs to the fungi, phylum Basidiomycetes, class Tremellales, order Tremellales, and genus Auricularia, etc. It is a kind of edible and medicinal fungus mainly distributed in China. It has a unique fruiting body flavor and high nutritional value, and contains many biologically active ingredients, including polysaccharides, active proteins, β-carotene and flavonoids. It has high edible and medicinal value, including antioxidant, anti-inflammatory, anti-tumor and immunomodulatory functions. Therefore, golden ear is becoming more and more popular among consumers, and its proportion in the diet of Chinese residents is increasing year by year. The surface of the mature golden ear fruiting body is bright orange-yellow, with excellent appearance. However, due to the instability of pigment substances, the color of golden ear is prone to fade during storage and processing, which not only affects its appearance and commodity value, but also affects its flavor and nutritional value.

[0003] At present, color protection agents containing sulfur dioxide (such as sodium metabisulfite and sodium pyrosulfite) are often used to protect the color of edible fungi during the production process. Although this method has the characteristics of good color protection effect and low price, it will cause sulfur dioxide residue during use, which will affect the health of consumers. Therefore, some people are also studying and exploring sulfur-free treatment technology. The Chinese patent with publication number CN101156622A discloses a sulfur-free drying process for fruits, vegetables and edible fungi with high rehydration, which is to slice the fruits, vegetables or edible fungi after sorting and washing, and then blanch them at high temperature, and then put the blanched fruits, vegetables or edible fungi into a solution containing 0.1%-0.5% citric acid and 0.02%-0.1% cysteine, and promote color protection by ultrasonic treatment for 5-15 minutes. This color protection technology is a pre-treatment step of the drying process, and its process is relatively complicated, and it is mainly used for fruits, vegetables and edible fungi with high rehydration. However, in view of the poor rehydration performance of dried golden ear products, the main processing and sales forms of golden ear in the market are still focused on fresh products. Therefore, this specific color protection technology is not suitable for the color protection treatment of golden ear. The Chinese patent with publication number CN102119713A discloses a method for processing and preserving edible fungi, which is to place the fresh edible fungi that have been removed from impurities and graded in a salt solution for ultrasonic dynamic cleaning treatment and then place them in a citric acid solution for ultrasonic dynamic color protection treatment. This method relies on a single citric acid solution for color protection treatment and is suitable for color protection treatment of ordinary edible fungi. However, given that the surface of golden ear in the mature stage presents a bright orange-yellow color, the carotenoids and other pigment components that give the orange-yellow color are richer than other edible fungi, and therefore, it is more prone to fading. Therefore, it is difficult to achieve the desired expected effect by relying solely on citric acid for color protection treatment.

[0004] Up to now, there has been no ideal method for protecting the color of golden ear mushrooms that is simple to operate, low in cost, safe, and has good color protection effects in the industry. Summary of the invention

[0005] The purpose of the present invention is to solve the deficiencies of the above-mentioned prior art and to provide a method for protecting the apparent sulfur-free color of mature golden ear fruiting bodies which is simple to operate, low in cost, safe and has good color protection effect, so as to solve the fading problem in the traditional golden ear storage and processing production process and extend the shelf life of the golden ear.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A method for protecting the apparent sulfur-free color of mature Tremella fuciformis fruiting bodies, the method being as follows:

[0008] 1) Use 30 mg / mL of food-grade L-malic acid and citric acid in a mass ratio of 2:1 or 1:2 to prepare a composite color preservative;

[0009] 2) Cut the golden ear fruiting bodies into even pieces and soak them in a compound color preservative for 20 minutes.

[0010] The applicant has found through research that the color change of golden ear is mainly due to the degradation of the natural pigments (mainly carotenoids) contained in it during processing or storage due to the influence of factors such as light. The main factor for the fading of golden ear fruiting bodies is ultraviolet light irradiation. Based on this main factor, the present invention has studied and obtained a method for apparent sulfur-free color protection of mature golden ear fruiting bodies. The golden ear fruiting bodies treated by the method of the present invention were placed under ultraviolet light for 10 hours, and the color value was measured by a colorimeter. There was no obvious fading phenomenon, and the original orange-yellow color of the mature golden ear fruiting bodies was retained to the greatest extent, which played an obvious color protection role for the mature golden ear fruiting bodies.

[0011] The color protection method of the present invention uses low-priced and highly safe food-grade additives, has the advantages of simple operation, low cost, and no sulfur dioxide, and provides an optimal composite color protection agent ratio, which can retain the original orange-yellow color of the mature golden ear fruiting body to a greater extent, prevent obvious fading and whitening, solve the color change problem of the golden ear fruiting body during storage and processing, extend the shelf life, further enhance the value of the golden ear in subsequent development and application, and ensure the sustainable development of the golden ear industry. The present invention uses a non-sulfur color protection method to preserve and process fresh golden ear fruiting bodies, which can avoid the use of sulfur dioxide-type bleaching agents, reduce the residual sulfur dioxide in the product, and improve food safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The types and contents of carotenoids contained in the fruiting bodies of Tremella truncatula at different growth stages;

[0013] Figure 2 is the standard curve of β-carotene;

[0014] Figure 3 This is the degradation rate change diagram of β-carotene under ultraviolet light;

[0015] Figure 4 This is the degradation rate change diagram of β-carotene under white light irradiation;

[0016] Figure 5 This is a comparison chart of the apparent chromaticity values ​​of the golden ear in the color-protecting agent treatment group and the blank group (distilled water);

[0017] Figure 6 This is a comparison chart of the appearance of golden ear treated with color preservative and the blank group (distilled water). DETAILED DESCRIPTION

[0018] The content of the present invention will be further described below in conjunction with specific embodiments.

[0019] Main materials and reagents:

[0020] Acetone, methanol, acetonitrile, formic acid, methyl tert-butyl ether, 2,6-di-tert-butyl-p-cresol (BHT) and n-hexane were all chromatographically pure and purchased from Merck Co., Ltd.; anhydrous ethanol, sodium chloride and potassium hydroxide were all analytically pure and purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd.; β-carotene was purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd.; food-grade D-isoascorbic acid, L-malic acid, citric acid and ascorbic acid were all purchased from Beijing Cuifeng Technology Co., Ltd.

[0021] Three different growth periods of golden ear fruiting bodies (from Yunnan Junshijie Biotechnology Co., Ltd.) were selected, including 25 days, 35 days and 45 days, and their apparent chromaticity values ​​were detected and analyzed using a colorimeter (Beijing Biotech Co., Ltd.). The average value of the three measurements was taken as the chromaticity value of the sample. At the same time, sensory judgment was used to observe the color changes of the samples with the naked eye to eliminate the possible errors caused by instrumental measurement.

[0022] Comparison of chromaticity values ​​at different growth stages: The chromaticity values ​​of the golden ear fruiting bodies at three different growth stages were measured, and the results are shown in Table 1.

[0023] Table 1 Comparison of chromaticity values ​​of golden ear fruiting bodies at three different growth stages

[0024]

[0025] Among them, the L* value indicates the brightness of the surface color, which mainly depends on the reflectivity of the product surface. The larger the L* value, the whiter the sample color. The a* value indicates the redness and greenness of the surface. By measuring the a* value of the sample surface, we can understand the degree to which the sample is biased towards red or green. The larger the a* value, the more red the sample color is. The b* value indicates the yellowness and blueness of the surface color. By measuring the b* value of the sample surface, we can understand the degree to which the sample is biased towards yellow or blue. The larger the b* value, the more yellow the sample color is. The larger the ∆E, the greater the color difference, and the easier it is to easily distinguish the difference between the color and the standard color. The formula for the total color difference value is as follows:

[0026]

[0027] In the above formula, Refers to the color difference between each group of samples. It refers to the difference in brightness between samples in each group. It refers to the difference in redness and greenness between samples in each group. b refers to the difference in yellow-blue tint between samples in each group.

[0028] As can be seen from Table 1, the apparent color of the golden ear fruiting bodies at different growth stages was measured by a colorimeter. It was found that with the extension of the growth cycle, the red-green color a* and the yellow-blue color b* of the golden ear increased significantly, reaching the highest at 45 days, which was consistent with the trend observed with the naked eye.

[0029] Calculate the color difference between each group of samples ( ), compared with the golden ear fruiting body with a growth period of 25 days, the color difference value of the golden ear fruiting body with a growth period of 35 days is 1 is lower, which is 2.96; compared with the golden ear fruiting body with a growth period of 25 days, the color difference value of the golden ear fruiting body with a growth period of 45 days is 2 is 45.98, much larger than 1; Combined with sensory evaluation, the fruiting bodies of golden ear with a growth period of 25 days and 35 days showed a lighter beige color, and only the fruiting bodies of golden ear with a growth period of 45 days (maturity) showed obvious orange-yellow color. Therefore, the apparent orange-yellow color of golden ear fruiting bodies mainly accumulated between 35 and 45 days (late stage of fruiting body growth).

[0030] Sample preparation:

[0031] (1) The fruiting bodies of Tremella truncatula at different growth stages were dried and ground into powder using a ball mill (MM400, Retsch, Germany) (30 Hz, 1 min);

[0032] (2) Weigh 50 mg of the ground sample using an electronic balance (AS 60 / 220.R2, RADWAG, Poland, Europe) and extract it with 0.5 mL of a mixed solution of n-hexane / acetone / ethanol (1:1:1, v / v / v) containing 0.01% BHT (g / mL);

[0033] (3) After vortexing (MIX-200, Shanghai Jingxin Industrial Development Co., Ltd.) at room temperature for 20 min, centrifuge at 12,000 g for 5 min at 4°C, take the supernatant, repeat the extraction once, and centrifuge (5424R, Eppendorf, Germany) to combine the supernatants;

[0034] (4) The extract was concentrated (CentriVap, LABCONCO, USA), reconstituted with 100 μL of a methanol / methyl tert-butyl ether mixture (1:1, v / v), filtered through a 0.22 μm filter membrane, and stored in a brown injection bottle for LC-MS / MS (SCIEX, USA) analysis.

[0035] Chromatography mass spectrometry acquisition conditions:

[0036] The data acquisition instrument system mainly includes ultra-high performance liquid chromatography (UPLC) and tandem mass spectrometry (MS / MS).

[0037] The liquid phase conditions mainly include:

[0038] (1) Chromatographic column: YMC C30 (3 μm, 100 mm × 2.0 mm);

[0039] (2) Mobile phase: Phase A, methanol / acetonitrile (1:3, v / v) with 0.01% BHT and 0.1% formic acid; Phase B, methyl tert-butyl ether with 0.01% BHT;

[0040] (3) Gradient elution program: A / B was 100:0 (V / V) at 0 min, 100:0 (V / V) at 3 min, 30:70 (V / V) at 5 min, 5:95 (V / V) at 9 min, 100:0 (V / V) at 10 min, and 100:0 (V / V) at 11 min;

[0041] (4) Flow rate: 0.8 mL / min; column temperature: 28°C; injection volume: 2 μL.

[0042] Mass spectrometry conditions mainly include:

[0043] The atmospheric pressure chemical ionization source (APCI) temperature was 350°C and the curtain gas (CUR) was 25 psi. In the Q-Trap 6500+, each ion pair was scanned and detected according to the optimized declustering potential (DP) and collision energy (CE).

[0044] Data processing: Substitute the integrated peak area of ​​all detected samples into the linear equation of the standard curve for calculation, and then further substitute it into the calculation formula to finally obtain the content data of the substance in the actual sample.

[0045] Carotenoid content in the sample (μg / g) = c*V / 1000 / m;

[0046] c is the concentration value (μg / mL) obtained by substituting the integrated peak area in the sample into the standard curve;

[0047] V is the volume of the solution used for reconstitution (μL);

[0048] m is the mass of the sample weighed (g).

[0049] Carotenoids are a general term for a class of natural pigments that are widely present in nature, including β-carotene, lycopene, α-carotene and lutein. They are natural powerful antioxidants and free radical scavengers, and are also involved in plant metabolic processes such as photosynthesis, photoprotection, growth and development.

[0050] LC-MS / MS analysis results are as follows Figure 1 As shown:

[0051] A total of 16 carotenoids were identified in the fruiting bodies of golden ear, mainly including carotene and lutein. During the growth period of 25-35 days, the contents of β-carotene, α-carotene, γ-carotene, phytoene, β-cryptoxanthin and other substances in the fruiting bodies of golden ear showed a certain increasing trend; during the growth period of 35-45 days, the above substances increased significantly in multiples, which was consistent with the trend of chromaticity and color difference value of golden ear. Therefore, the apparent orange-yellow color of golden ear is mainly formed by the gradual and balanced accumulation of orange-red carotene and yellow lutein during the growth process, and the enrichment of this type of substance is consistent with the trend of the apparent color, mainly concentrated between 35-45 days. The golden ear fruiting bodies of 45 days (mature stage) showed obvious orange-yellow color and the highest content of carotenoids, and were also most prone to fading. Therefore, color protection treatment is required for the mature golden ear fruiting bodies.

[0052] The content of β-carotene in the fruiting body of golden ear is the highest, accounting for more than 70% of the total carotene content. Therefore, the main factors affecting the apparent color stability of golden ear were explored with β-carotene content as a characteristic indicator.

[0053] The orange-yellow color of golden ear may be positively correlated with its carotenoid content, and the β-carotene content is the highest (>70%) in golden ear at 45 days (maturity), so the mature golden ear fruiting bodies were selected as the research object, and β-carotene was used as a characteristic indicator to study the effect of different light on its stability. β-carotene is a conjugated double bond composed of isoprene residues. It has very good light absorption performance in the band range of 450-550 nm (blue-green in the visible light spectrum) and can play an important role in photosynthesis as a natural pigment. β-carotene is also the main component of yellow and orange fruits. Because it contains a large number of C=C conjugated systems between its molecules, it is very easy to undergo cis-trans isomerization and oxidative degradation under light conditions, making the pigment unstable.

[0054] Therefore, the β-carotene in the fruiting bodies of golden ear was taken as the research object, and it was extracted and prepared to explore the effect of light (white light and ultraviolet light) on the β-carotene in the fruiting bodies of golden ear. The specific steps are as follows:

[0055] (1) The 45-day-old Tremella fuciformis fruiting body powder was mixed with acetone:ethanol (1:1, v:v) at a solid-liquid ratio of 1:5 (w / v, g / mL). After mixing, the mixture was wrapped in tin foil and sonicated in the dark (KQ5200E, Kunshan Shumei Ultrasonic Instrument Co., Ltd.) for 30 min. The mixture was centrifuged at 8000 g for 20 min, and the supernatant was placed in a microplate reader (Synergy HT, BIO-TEK, USA) to detect the absorbance at 450 nm.

[0056] (2) Using β-carotene as the standard, the concentrations were set at 10.0, 7.5, 5.0, 2.5, 1.0, and 0.0 μg / mL, and the following was obtained: Figure 2 β-carotene standard curve shown;

[0057] (3) Divide the supernatant in step 1 into two groups, 8 mL each (three parallels), a UV light irradiation group and a white light irradiation group;

[0058] (4) The absorbance of the UV-irradiated group was measured every 2 hours for a total of 24 hours; the absorbance of the white-light-irradiated group was measured every week for a total of 3 weeks. The absorbance was substituted into the standard curve to obtain the β-carotene content, and a curve was drawn based on the degradation rate of β-carotene under UV-light and white-light irradiation.

[0059] from Figure 3 It can be seen that with the extension of UV irradiation time, β-carotene is extremely unstable. From 0 to 10 h, its degradation rate increases linearly. At about 10 h, the degradation rate of β-carotene has reached 100%, which is basically completely degraded. Figure 4 It can be seen that the degradation rate of β-carotene can reach about 90% after 3 weeks of white light irradiation. Compared with ultraviolet light irradiation, the degradation rate of β-carotene under white light irradiation is slower. Therefore, ultraviolet light is the main factor causing the degradation of β-carotene in golden ear.

[0060] The above research by the applicant shows that the color change of golden ear is mainly due to the degradation of the natural pigments (mainly carotenoids) contained in it due to the influence of factors such as light during processing or storage, and the main factor for the fading of golden ear fruiting bodies is ultraviolet light.

[0061] Based on the above research foundation, different types and concentrations of color preservatives were screened for experimental comparison. The test samples were irradiated with ultraviolet light for 10 hours, and the effect of the color preservatives on the color of the golden ear fruiting bodies was determined based on the changes in their chromaticity values. The specific steps are as follows:

[0062] (1) At the same concentration, a certain amount of citric acid, L-malic acid, ascorbic acid, and sodium D-isoascorbate were dissolved in distilled water at a concentration of 30 mg / mL as the experimental group, and an equal amount of distilled water was used as the blank group. The evenly cut Tremella fuciformis fruiting bodies were immersed in them for 20 min, and then irradiated with ultraviolet light for 10 h, and the color value was measured using a colorimeter;

[0063] (2) The two best single color preservatives, citric acid and L-malic acid, were screened out and mixed in the ratios of 1:1, 2:1, 3:1, 4:1, 5:1, 1:2, 1:3, 1:4 and 1:5, respectively. Distilled water was used as the blank group and the cut uniform golden ear fruiting bodies were immersed in it for 20 min. After irradiation with ultraviolet light, the color protection effects of different composite color preservatives were compared.

[0064] Table 2 shows the effect of different types of color preservatives on the apparent chromaticity of the golden ear fruiting bodies. In the table, the a* value indicates the red-green color of the surface. By measuring the a* value of the sample surface, we can understand the degree to which the sample is biased towards red or green. The larger the a* value, the more red the sample color is. b* indicates the yellow-blue color of the surface color. By measuring the b* value of the sample surface, we can understand the degree to which the sample is biased towards yellow or blue. The larger the b* value, the more yellow the sample is. The higher the a* and b* values, the more obvious the orange-yellow color is.

[0065] As can be seen from Table 2, the a* and b* values ​​of the golden ear fruiting bodies in the blank group (distilled water) were significantly reduced, and obvious fading and whitening were observed with the naked eye. Compared with ascorbic acid and sodium L-isoascorbate, the golden ear fruiting bodies treated with citric acid and L-malic acid for color protection showed obvious exudation and poor resilience after being irradiated with ultraviolet light and combined with sensory evaluation. Therefore, citric acid and L-malic acid can better maintain the original color and appearance of golden ear fruiting bodies.

[0066] Table 2 Effects of different types of color preservatives on the apparent chromaticity of Tremella truncatula fruiting bodies

[0067]

[0068] The larger the chromaticity value L* value, the whiter the sample color, the larger the a* value, the redder the sample color, and the larger the b* value, the yellower the sample color. The color of golden ear is mainly orange-yellow, so in this embodiment, the a* and b* values ​​are analyzed to determine the color change of golden ear under different color protection agent treatments.

[0069] The color protection effect of different proportions of L-malic acid and citric acid was investigated. Table 3 shows the effect of different proportions of L-malic acid and citric acid on the apparent chromaticity value of golden ear fruiting body. Figure 5This is a comparison chart of the apparent chromaticity values ​​of the golden ear in the color-protecting agent treatment group and the blank group (distilled water). Figure 5 In the figure, color preservative 1 and color preservative 2 are L-malic acid and citric acid in a mass ratio of 2:1 and 1:2, respectively. The a* value represents the red-green color of the sample surface, and the b* represents the yellow-blue color of the sample surface.

[0070] From Table 3 and Figure 5 It can be seen that after UV irradiation, the a* and b* values ​​of the golden ear fruiting bodies in the blank group (distilled water) were significantly reduced, and the naked eye observed obvious fading and whitening; after the color protection treatment with different proportions of L-malic acid and citric acid, the a* and b* values ​​of the golden ear fruiting bodies increased significantly, and the surface of the golden ear fruiting bodies showed different degrees of orange-yellow color when observed with the naked eye, which can maintain the apparent color of the golden ear. The mixed ratio of color protectant is better than that of single color protection treatment, and the effect of L-malic acid: citric acid is better at 2:1 and 1:2 respectively. The color protection agent treatment can maximize the orange-yellow color of the golden ear fruiting bodies in the mature stage, and will not be affected by UV irradiation during storage and processing.

[0071] Figure 6 This is a comparison chart of the appearance of golden ear treated with color preservative and the blank group (distilled water). Figure 6 In the figure, A is the appearance of the golden ear treated with distilled water after being irradiated with UV light; B is the appearance of the golden ear treated with color protectant 1 (L-malic acid and citric acid mass ratio 2:1) after being irradiated with UV light; C is the appearance of the golden ear treated with color protectant 2 (L-malic acid and citric acid mass ratio 1:2) after being irradiated with UV light. In the figure, A shows obvious whitening and fading on the surface by naked eye observation, while the golden ear fruiting bodies B and C treated with color protectants have obvious orange-yellow color on the surface.

[0072] Table 3 Effects of different ratios of L-malic acid and citric acid on the apparent chromaticity of Tremella truncatula fruiting bodies

[0073]

[0074] Based on the above research analysis and experimental verification, the following simple, low-cost, safe and effective method for the apparent sulfur-free color protection of mature golden ear fruiting bodies was determined, namely: 1) 30 mg / mL of edible-grade L-malic acid and citric acid were used in a mass ratio of 2:1 or 1:2 to prepare a composite color protection agent; 2) the golden ear fruiting bodies were evenly cut into pieces and soaked in the composite color protection agent for 20 minutes. This method can make the golden ear fruiting bodies still show obvious orange-yellow color under ultraviolet light, slowing down possible fading. After the color protection treatment, the golden ear fruiting bodies show the best orange-yellow color, preventing fading due to long-term exposure during subsequent processing and storage, and extending the shelf life of the golden ear.

[0075] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for protecting the apparent sulfur-free color of mature Tremella fuciformis fruiting bodies, characterized in that: The method is as follows: 1) 30 mg / mL of food-grade L-malic acid and citric acid are used in a mass ratio of 2:1 or 1:2 to prepare a composite color preservative; 2) Cut the golden ear fruiting bodies into even pieces and soak them in a compound color preservative for 20 minutes.

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